Dashboard Studio 1.6.1: show version, load fresh files after updates

- Version shown under About in the dashboard settings, with a link to
  the repository; /api/version reports it
- index.html is never cached and stamps the version on every asset URL,
  so browsers can't keep running old files after an update
- Open screens check the version after reconnecting and every 5 minutes
  and reload into the new version (editing only shows a message);
  pending saves are flushed first

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

dashboard_studio/config.yaml

@@ -1,5 +1,5 @@
 name: Dashboard Studio
-version: "1.6.0"
+version: "1.6.1"
 slug: dashboard_studio
 description: Drag-and-drop dashboard builder with a free-form grid, live entity widgets and themes.
 url: https://git.melvanveen.nl/veenm/ha-dashboard-studio